add migration guide

Author: vcc-sanya

MIGRATION.md

@@ -0,0 +1,16 @@
+## Migration to v0.5 (HA v0.115)
+Before version 0.5 we used fixed network options, now we are using network options from the config.
+
+If you want to upgrade from 0.4 to 0.5 you have two options:
+1. Repair you devices
+2. Add network options to config
+
+```yaml
+zha:
+  zigpy_config:
+    network:
+      channel: 11
+      channels: [11]
+      pan_id: 0x1A62
+      extended_pan_id: "DD:DD:DD:DD:DD:DD:DD:DD"
+```

README.md

@@ -13,6 +13,9 @@ zigpy-cc allows Zigpy to interact with Texas Instruments ZNP (Zigbee Network Pro
 
 The zigpy-cc library itself initially began as a code port from the [zigbee-herdsman](https://github.com/Koenkk/zigbee-herdsman/tree/v0.12.24) project (version 0.12.24) for the [Zigbee2mqtt](https://www.zigbee2mqtt.io/) project by Koen Kanters (a.k.a. Koenkk GitHub). The zigbee-herdsman library itself in turn was originally a fork and rewrite of the [zigbee-shepherd](https://github.com/zigbeer/zigbee-shepherd) library by the [Zigbeer](https://github.com/zigbeer) project. Therefore, if the upstream code improvements or bug-fixes gets commited to the [zigbee-herdsman](https://github.com/Koenkk/zigbee-herdsman) library then it could, in theory, also be possible to downport some or many of those upstream code improvements to this zigpy-cc library for its benifit.
 
+## Migration to v0.5 (HA v0.115)
+See: [Migration guide](./MIGRATION.md)
+
 ## WARNING!!! - Work in progress
 Disclaimer: This software is provided "AS IS", without warranty of any kind. The zigpy-cc project is under development as WIP (work in progress), it is not fully working yet.